As promised, here's the list of places where the wrong Latin-1 encoding spelling is used:

Lib//test/test_cmd_line.py:
--         for encoding in ('ascii', 'latin1', 'utf8'):
Lib//test/test_codecs.py:
--         ef = codecs.EncodedFile(f, 'utf-8', 'latin1')
Lib//test/test_shelve.py:
--         shelve.Shelf(d, keyencoding='latin1')[key] = [1]
--         self.assertIn(key.encode('latin1'), d)
Lib//test/test_uuid.py:
--             os.write(fds[1], value.hex.encode('latin1'))
--             child_value = os.read(fds[0], 100).decode('latin1')
Lib//test/test_xml_etree.py:
--     >>> ET.tostring(ET.PI('test', '<testing&>\xe3'), 'latin1')
--     b"<?xml version='1.0' encoding='latin1'?>\\n<?test <testing&>\\xe3?>"
Lib//urllib/request.py:
--             data = base64.decodebytes(data.encode('ascii')).decode('latin1')
Lib//asynchat.py:
--     encoding                = 'latin1'
Lib//sre_parse.py:
--         encode = lambda x: x.encode('latin1')
Lib//distutils/command/bdist_wininst.py:
--             # convert back to bytes. "latin1" simply avoids any possible
--                 encoding="latin1") as script:
--                 script_data = script.read().encode("latin1")
Lib//test/test_bigmem.py:
--         return s.encode("latin1")
--         return bytearray(s.encode("latin1"))
Lib//test/test_bytes.py:
--         self.assertRaises(UnicodeEncodeError, self.type2test, sample, "latin1")
--         b = self.type2test(sample, "latin1", "ignore")
--         b = self.type2test(sample, "latin1")
Lib//test/test_codecs.py:
--         self.assertEqual("\udce4\udceb\udcef\udcf6\udcfc".encode("latin1", "surrogateescape"),
Lib//test/test_io.py:
--     with open(__file__, "r", encoding="latin1") as f:
--         t.__init__(b, encoding="latin1", newline="\r\n")
--         self.assertEqual(t.encoding, "latin1")
--             for enc in "ascii", "latin1", "utf8" :# , "utf-16-be", "utf-16-le":
Lib//ftplib.py:
--     encoding = "latin1"

I'll fix those later today or tomorrow.